%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
TcSplice: Template Haskell splices
\begin{code}
module TcSplice( kcSpliceType, tcSpliceExpr, tcSpliceDecls, tcBracket,
lookupThName_maybe,
runQuasiQuoteExpr, runQuasiQuotePat,
runQuasiQuoteDecl, runQuasiQuoteType,
runAnnotation ) where
#include "HsVersions.h"
import HscMain
import TcRnDriver
import HsSyn
import Convert
import RnExpr
import RnEnv
import RdrName
import RnTypes
import TcPat
import TcExpr
import TcHsSyn
import TcSimplify
import TcUnify
import Type
import Kind
import TcType
import TcEnv
import TcMType
import TcHsType
import TcIface
import TypeRep
import FamInst
import FamInstEnv
import InstEnv
import Name
import NameEnv
import NameSet
import PrelNames
import HscTypes
import OccName
import Var
import Module
import Annotations
import TcRnMonad
import Class
import Inst
import TyCon
import DataCon
import TcEvidence( TcEvBinds(..) )
import Id
import IdInfo
import DsMeta
import DsExpr
import DsMonad hiding (Splice)
import Serialized
import ErrUtils
import SrcLoc
import Outputable
import Util ( dropList )
import Data.List ( mapAccumL )
import Pair
import Unique
import Data.Maybe
import BasicTypes
import Panic
import FastString
import Control.Monad ( when )
import qualified Language.Haskell.TH as TH
import qualified Language.Haskell.TH.Syntax as TH
#ifdef GHCI
import GHC.Desugar ( AnnotationWrapper(..) )
#endif
import GHC.Exts ( unsafeCoerce# )
\end{code}
Note [How top-level splices are handled]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Top-level splices (those not inside a [| .. |] quotation bracket) are handled
very straightforwardly:
1. tcTopSpliceExpr: typecheck the body e of the splice $(e)
2. runMetaT: desugar, compile, run it, and convert result back to
HsSyn RdrName (of the appropriate flavour, eg HsType RdrName,
HsExpr RdrName etc)
3. treat the result as if that's what you saw in the first place
e.g for HsType, rename and kind-check
for HsExpr, rename and type-check
(The last step is different for decls, becuase they can *only* be
top-level: we return the result of step 2.)
Note [How brackets and nested splices are handled]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Nested splices (those inside a [| .. |] quotation bracket), are treated
quite differently.
* After typechecking, the bracket [| |] carries
a) A mutable list of PendingSplice
type PendingSplice = (Name, LHsExpr Id)
b) The quoted expression e, *renamed*: (HsExpr Name)
The expression e has been typechecked, but the result of
that typechecking is discarded.
* The brakcet is desugared by DsMeta.dsBracket. It
a) Extends the ds_meta environment with the PendingSplices
attached to the bracket
b) Converts the quoted (HsExpr Name) to a CoreExpr that, when
run, will produce a suitable TH expression/type/decl. This
is why we leave the *renamed* expression attached to the bracket:
the quoted expression should not be decorated with all the goop
added by the type checker
* Each splice carries a unique Name, called a "splice point", thus
${n}(e). The name is initialised to an (Unqual "splice") when the
splice is created; the renamer gives it a unique.
* When the type checker type-checks a nested splice ${n}(e), it
- typechecks e
- adds the typechecked expression (of type (HsExpr Id))
as a pending splice to the enclosing bracket
- returns something non-committal
Eg for [| f ${n}(g x) |], the typechecker
- attaches the typechecked term (g x) to the pending splices for n
in the outer bracket
- returns a non-committal type \alpha.
Remember that the bracket discards the typechecked term altogether
* When DsMeta (used to desugar the body of the bracket) comes across
a splice, it looks up the splice's Name, n, in the ds_meta envt,
to find an (HsExpr Id) that should be substituted for the splice;
it just desugars it to get a CoreExpr (DsMeta.repSplice).
Example:
Source: f = [| Just $(g 3) |]
The [| |] part is a HsBracket
Typechecked: f = [| Just ${s7}(g 3) |]{s7 = g Int 3}
The [| |] part is a HsBracketOut, containing *renamed*
(not typechecked) expression
The "s7" is the "splice point"; the (g Int 3) part
is a typechecked expression
Desugared: f = do { s7 <- g Int 3
; return (ConE "Data.Maybe.Just" s7) }
Note [Template Haskell state diagram]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here are the ThStages, s, their corresponding level numbers
(the result of (thLevel s)), and their state transitions.
----------- $ ------------ $
| Comp | ---------> | Splice | -----|
| 1 | | 0 | <----|
----------- ------------
^ | ^ |
$ | | [||] $ | | [||]
| v | v
-------------- ----------------
| Brack Comp | | Brack Splice |
| 2 | | 1 |
-------------- ----------------
* Normal top-level declarations start in state Comp
(which has level 1).
Annotations start in state Splice, since they are
treated very like a splice (only without a '$')
* Code compiled in state Splice (and only such code)
will be *run at compile time*, with the result replacing
the splice
* The original paper used level -1 instead of 0, etc.
* The original paper did not allow a splice within a
splice, but there is no reason not to. This is the
$ transition in the top right.
Note [Template Haskell levels]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Imported things are impLevel (= 0)
* In GHCi, variables bound by a previous command are treated
as impLevel, because we have bytecode for them.
* Variables are bound at the "current level"
* The current level starts off at outerLevel (= 1)
* The level is decremented by splicing $(..)
incremented by brackets [| |]
incremented by name-quoting 'f
When a variable is used, we compare
bind: binding level, and
use: current level at usage site
Generally
bind > use Always error (bound later than used)
[| \x -> $(f x) |]
bind = use Always OK (bound same stage as used)
[| \x -> $(f [| x |]) |]
bind < use Inside brackets, it depends
Inside splice, OK
Inside neither, OK
For (bind < use) inside brackets, there are three cases:
- Imported things OK f = [| map |]
- Top-level things OK g = [| f |]
- Non-top-level Only if there is a liftable instance
h = \(x:Int) -> [| x |]
See Note [What is a top-level Id?]
Note [Quoting names]
~~~~~~~~~~~~~~~~~~~~
A quoted name 'n is a bit like a quoted expression [| n |], except that we
have no cross-stage lifting (c.f. TcExpr.thBrackId). So, after incrementing
the use-level to account for the brackets, the cases are:
bind > use Error
bind = use OK
bind < use
Imported things OK
Top-level things OK
Non-top-level Error
See Note [What is a top-level Id?] in TcEnv. Examples:
f 'map -- OK; also for top-level defns of this module
\x. f 'x -- Not ok (whereas \x. f [| x |] might have been ok, by
-- cross-stage lifting
\y. [| \x. $(f 'y) |] -- Not ok (same reason)
[| \x. $(f 'x) |] -- OK
Note [What is a top-level Id?]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In the level-control criteria above, we need to know what a "top level Id" is.
There are three kinds:
* Imported from another module (GlobalId, ExternalName)
* Bound at the top level of this module (ExternalName)
* In GHCi, bound by a previous stmt (GlobalId)
It's strange that there is no one criterion tht picks out all three, but that's
how it is right now. (The obvious thing is to give an ExternalName to GHCi Ids
bound in an earlier Stmt, but what module would you choose? See
Note [Interactively-bound Ids in GHCi] in TcRnDriver.)
The predicate we use is TcEnv.thTopLevelId.
%************************************************************************
%* *
\subsection{Main interface + stubs for the non-GHCI case
%* *
%************************************************************************
\begin{code}
tcBracket :: HsBracket Name -> TcRhoType -> TcM (LHsExpr TcId)
tcSpliceDecls :: LHsExpr Name -> TcM [LHsDecl RdrName]
tcSpliceExpr :: HsSplice Name -> TcRhoType -> TcM (HsExpr TcId)
kcSpliceType :: HsSplice Name -> FreeVars -> TcM (HsType Name, TcKind)
lookupThName_maybe :: TH.Name -> TcM (Maybe Name)
runQuasiQuoteExpr :: HsQuasiQuote RdrName -> RnM (LHsExpr RdrName)
runQuasiQuotePat :: HsQuasiQuote RdrName -> RnM (LPat RdrName)
runQuasiQuoteType :: HsQuasiQuote RdrName -> RnM (LHsType RdrName)
runQuasiQuoteDecl :: HsQuasiQuote RdrName -> RnM [LHsDecl RdrName]
runAnnotation :: CoreAnnTarget -> LHsExpr Name -> TcM Annotation
#ifndef GHCI
tcBracket x _ = pprPanic "Cant do tcBracket without GHCi" (ppr x)
tcSpliceExpr e = pprPanic "Cant do tcSpliceExpr without GHCi" (ppr e)
tcSpliceDecls x = pprPanic "Cant do tcSpliceDecls without GHCi" (ppr x)
kcSpliceType x fvs = pprPanic "Cant do kcSpliceType without GHCi" (ppr x)
lookupThName_maybe n = pprPanic "Cant do lookupThName_maybe without GHCi" (ppr n)
runQuasiQuoteExpr q = pprPanic "Cant do runQuasiQuoteExpr without GHCi" (ppr q)
runQuasiQuotePat q = pprPanic "Cant do runQuasiQuotePat without GHCi" (ppr q)
runQuasiQuoteType q = pprPanic "Cant do runQuasiQuoteType without GHCi" (ppr q)
runQuasiQuoteDecl q = pprPanic "Cant do runQuasiQuoteDecl without GHCi" (ppr q)
runAnnotation _ q = pprPanic "Cant do runAnnotation without GHCi" (ppr q)
#else
\end{code}
%************************************************************************
%* *
\subsection{Quoting an expression}
%* *
%************************************************************************
\begin{code}
tcBracket brack res_ty
= addErrCtxt (hang (ptext (sLit "In the Template Haskell quotation"))
2 (ppr brack)) $
do {
cur_stage <- getStage
; checkTc (not (isBrackStage cur_stage)) illegalBracket
; recordThUse
; pending_splices <- newMutVar []
; lie_var <- getConstraintVar
; let brack_stage = Brack cur_stage pending_splices lie_var
; (_,lie) <- captureConstraints $
newImplication BracketSkol [] [] $
setStage brack_stage $
do { meta_ty <- tc_bracket cur_stage brack
; unifyType meta_ty res_ty }
; _ <- simplifyTop lie
; pendings <- readMutVar pending_splices
; return (noLoc (HsBracketOut brack pendings)) }
tc_bracket :: ThStage -> HsBracket Name -> TcM TcType
tc_bracket outer_stage br@(VarBr _ name)
= do { thing <- tcLookup name
; case thing of
AGlobal {} -> return ()
ATyVar {} -> return ()
ATcId { tct_level = bind_lvl, tct_id = id }
| thTopLevelId id
-> keepAliveTc id
| otherwise
-> do { checkTc (thLevel outer_stage + 1 == bind_lvl)
(quotedNameStageErr br) }
_ -> pprPanic "th_bracket" (ppr name $$ ppr thing)
; tcMetaTy nameTyConName
}
tc_bracket _ (ExpBr expr)
= do { any_ty <- newFlexiTyVarTy openTypeKind
; _ <- tcMonoExprNC expr any_ty
; tcMetaTy expQTyConName }
tc_bracket _ (TypBr typ)
= do { _ <- tcHsSigTypeNC ThBrackCtxt typ
; tcMetaTy typeQTyConName }
tc_bracket _ (DecBrG decls)
= do { _ <- tcTopSrcDecls emptyModDetails decls
; tcMetaTy decsQTyConName }
tc_bracket _ (PatBr pat)
= do { any_ty <- newFlexiTyVarTy openTypeKind
; _ <- tcPat ThPatQuote pat any_ty $
return ()
; tcMetaTy patQTyConName }
tc_bracket _ (DecBrL _)
= panic "tc_bracket: Unexpected DecBrL"
quotedNameStageErr :: HsBracket Name -> SDoc
quotedNameStageErr br
= sep [ ptext (sLit "Stage error: the non-top-level quoted name") <+> ppr br
, ptext (sLit "must be used at the same stage at which is is bound")]
\end{code}
%************************************************************************
%* *
\subsection{Splicing an expression}
%* *
%************************************************************************
\begin{code}
tcSpliceExpr (HsSplice name expr) res_ty
= setSrcSpan (getLoc expr) $ do
{ stage <- getStage
; case stage of {
Splice -> tcTopSplice expr res_ty ;
Comp -> tcTopSplice expr res_ty ;
Brack pop_stage ps_var lie_var -> do
{ meta_exp_ty <- tcMetaTy expQTyConName
; expr' <- setStage pop_stage $
setConstraintVar lie_var $
tcMonoExpr expr meta_exp_ty
; ps <- readMutVar ps_var
; writeMutVar ps_var ((name,expr') : ps)
; return (panic "tcSpliceExpr")
}}}
tcTopSplice :: LHsExpr Name -> TcRhoType -> TcM (HsExpr Id)
tcTopSplice expr res_ty
= do { meta_exp_ty <- tcMetaTy expQTyConName
; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
; expr2 <- runMetaE zonked_q_expr
; showSplice "expression" expr (ppr expr2)
; addErrCtxt (spliceResultDoc expr) $ do
{ (exp3, _fvs) <- checkNoErrs (rnLExpr expr2)
; exp4 <- tcMonoExpr exp3 res_ty
; return (unLoc exp4) } }
spliceResultDoc :: LHsExpr Name -> SDoc
spliceResultDoc expr
= sep [ ptext (sLit "In the result of the splice:")
, nest 2 (char '$' <> pprParendExpr expr)
, ptext (sLit "To see what the splice expanded to, use -ddump-splices")]
tcTopSpliceExpr :: TcM (LHsExpr Id) -> TcM (LHsExpr Id)
tcTopSpliceExpr tc_action
= checkNoErrs $
setStage Splice $
do {
(expr', lie) <- captureConstraints tc_action
; const_binds <- simplifyTop lie
; zonkTopLExpr (mkHsDictLet (EvBinds const_binds) expr') }
\end{code}
%************************************************************************
%* *
Splicing a type
%* *
%************************************************************************
Very like splicing an expression, but we don't yet share code.
\begin{code}
kcSpliceType splice@(HsSplice name hs_expr) fvs
= setSrcSpan (getLoc hs_expr) $ do
{ stage <- getStage
; case stage of {
Splice -> kcTopSpliceType hs_expr ;
Comp -> kcTopSpliceType hs_expr ;
Brack pop_level ps_var lie_var -> do
{ meta_ty <- tcMetaTy typeQTyConName
; expr' <- setStage pop_level $
setConstraintVar lie_var $
tcMonoExpr hs_expr meta_ty
; ps <- readMutVar ps_var
; writeMutVar ps_var ((name,expr') : ps)
; kind <- newMetaKindVar
; return (HsSpliceTy splice fvs kind, kind)
}}}
kcTopSpliceType :: LHsExpr Name -> TcM (HsType Name, TcKind)
kcTopSpliceType expr
= do { meta_ty <- tcMetaTy typeQTyConName
; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_ty)
; hs_ty2 <- runMetaT zonked_q_expr
; showSplice "type" expr (ppr hs_ty2)
; addErrCtxt (spliceResultDoc expr) $ do
{ let doc = SpliceTypeCtx hs_ty2
; hs_ty3 <- checkNoErrs (rnLHsType doc hs_ty2)
; (ty4, kind) <- kcLHsType hs_ty3
; return (unLoc ty4, kind) }}
\end{code}
%************************************************************************
%* *
\subsection{Splicing an expression}
%* *
%************************************************************************
\begin{code}
tcSpliceDecls expr
= do { list_q <- tcMetaTy decsQTyConName
; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr list_q)
; decls <- runMetaD zonked_q_expr
; showSplice "declarations" expr
(ppr (getLoc expr) $$ (vcat (map ppr decls)))
; return decls }
\end{code}
%************************************************************************
%* *
Annotations
%* *
%************************************************************************
\begin{code}
runAnnotation target expr = do
loc <- getSrcSpanM
data_class <- tcLookupClass dataClassName
to_annotation_wrapper_id <- tcLookupId toAnnotationWrapperName
zonked_wrapped_expr' <- tcTopSpliceExpr $
do { (expr', expr_ty) <- tcInferRhoNC expr
; wrapper <- instCall AnnOrigin [expr_ty] [mkClassPred data_class [expr_ty]]
; let specialised_to_annotation_wrapper_expr
= L loc (HsWrap wrapper (HsVar to_annotation_wrapper_id))
; return (L loc (HsApp specialised_to_annotation_wrapper_expr expr')) }
flip runMetaAW zonked_wrapped_expr' $ \annotation_wrapper ->
case annotation_wrapper of
AnnotationWrapper value | let serialized = toSerialized serializeWithData value ->
seqSerialized serialized `seq` Annotation {
ann_target = target,
ann_value = serialized
}
\end{code}
%************************************************************************
%* *
Quasi-quoting
%* *
%************************************************************************
Note [Quasi-quote overview]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
The GHC "quasi-quote" extension is described by Geoff Mainland's paper
"Why it's nice to be quoted: quasiquoting for Haskell" (Haskell
Workshop 2007).
Briefly, one writes
[p| stuff |]
and the arbitrary string "stuff" gets parsed by the parser 'p', whose
type should be Language.Haskell.TH.Quote.QuasiQuoter. 'p' must be
defined in another module, because we are going to run it here. It's
a bit like a TH splice:
$(p "stuff")
However, you can do this in patterns as well as terms. Becuase of this,
the splice is run by the *renamer* rather than the type checker.
%************************************************************************
%* *
\subsubsection{Quasiquotation}
%* *
%************************************************************************
See Note [Quasi-quote overview] in TcSplice.
\begin{code}
runQuasiQuote :: Outputable hs_syn
=> HsQuasiQuote RdrName
-> Name
-> Name
-> MetaOps th_syn hs_syn
-> RnM hs_syn
runQuasiQuote (HsQuasiQuote quoter q_span quote) quote_selector meta_ty meta_ops
= do {
let occ_str = occNameString (rdrNameOcc quoter)
; quoter <- ASSERT( not (null occ_str) )
if head occ_str /= '$' then return quoter
else do { addWarn (deprecatedDollar quoter)
; return (mkRdrUnqual (mkVarOcc (tail occ_str))) }
; quoter' <- lookupOccRn quoter
; when (isUnboundName quoter') failM
; this_mod <- getModule
; let is_local = nameIsLocalOrFrom this_mod quoter'
; checkTc (not is_local) (quoteStageError quoter')
; traceTc "runQQ" (ppr quoter <+> ppr is_local)
; let quoterExpr = L q_span $! HsVar $! quoter'
; let quoteExpr = L q_span $! HsLit $! HsString quote
; let expr = L q_span $
HsApp (L q_span $
HsApp (L q_span (HsVar quote_selector)) quoterExpr) quoteExpr
; meta_exp_ty <- tcMetaTy meta_ty
; zonked_q_expr <- tcTopSpliceExpr (tcMonoExpr expr meta_exp_ty)
; result <- runMetaQ meta_ops zonked_q_expr
; showSplice (mt_desc meta_ops) quoteExpr (ppr result)
; return result }
runQuasiQuoteExpr qq = runQuasiQuote qq quoteExpName expQTyConName exprMetaOps
runQuasiQuotePat qq = runQuasiQuote qq quotePatName patQTyConName patMetaOps
runQuasiQuoteType qq = runQuasiQuote qq quoteTypeName typeQTyConName typeMetaOps
runQuasiQuoteDecl qq = runQuasiQuote qq quoteDecName decsQTyConName declMetaOps
quoteStageError :: Name -> SDoc
quoteStageError quoter
= sep [ptext (sLit "GHC stage restriction:") <+> ppr quoter,
nest 2 (ptext (sLit "is used in a quasiquote, and must be imported, not defined locally"))]
deprecatedDollar :: RdrName -> SDoc
deprecatedDollar quoter
= hang (ptext (sLit "Deprecated syntax:"))
2 (ptext (sLit "quasiquotes no longer need a dollar sign:")
<+> ppr quoter)
\end{code}
%************************************************************************
%* *
\subsection{Running an expression}
%* *
%************************************************************************
\begin{code}
data MetaOps th_syn hs_syn
= MT { mt_desc :: String
, mt_show :: th_syn -> String
, mt_cvt :: SrcSpan -> th_syn -> Either Message hs_syn
}
exprMetaOps :: MetaOps TH.Exp (LHsExpr RdrName)
exprMetaOps = MT { mt_desc = "expression", mt_show = TH.pprint, mt_cvt = convertToHsExpr }
patMetaOps :: MetaOps TH.Pat (LPat RdrName)
patMetaOps = MT { mt_desc = "pattern", mt_show = TH.pprint, mt_cvt = convertToPat }
typeMetaOps :: MetaOps TH.Type (LHsType RdrName)
typeMetaOps = MT { mt_desc = "type", mt_show = TH.pprint, mt_cvt = convertToHsType }
declMetaOps :: MetaOps [TH.Dec] [LHsDecl RdrName]
declMetaOps = MT { mt_desc = "declarations", mt_show = TH.pprint, mt_cvt = convertToHsDecls }
runMetaAW :: Outputable output
=> (AnnotationWrapper -> output)
-> LHsExpr Id
-> TcM output
runMetaAW k = runMeta False (\_ -> return . Right . k)
runMetaQ :: Outputable hs_syn
=> MetaOps th_syn hs_syn
-> LHsExpr Id
-> TcM hs_syn
runMetaQ (MT { mt_show = show_th, mt_cvt = cvt }) expr
= runMeta True run_and_cvt expr
where
run_and_cvt expr_span hval
= do { th_result <- TH.runQ hval
; traceTc "Got TH result:" (text (show_th th_result))
; return (cvt expr_span th_result) }
runMetaE :: LHsExpr Id
-> TcM (LHsExpr RdrName)
runMetaE = runMetaQ exprMetaOps
runMetaT :: LHsExpr Id
-> TcM (LHsType RdrName)
runMetaT = runMetaQ typeMetaOps
runMetaD :: LHsExpr Id
-> TcM [LHsDecl RdrName]
runMetaD = runMetaQ declMetaOps
runMeta :: (Outputable hs_syn)
=> Bool
-> (SrcSpan -> x -> TcM (Either Message hs_syn))
-> LHsExpr Id
-> TcM hs_syn
runMeta show_code run_and_convert expr
= do { traceTc "About to run" (ppr expr)
; recordThSpliceUse
; failIfErrsM
; ds_expr <- initDsTc (dsLExpr expr)
; hsc_env <- getTopEnv
; src_span <- getSrcSpanM
; traceTc "About to run (desugared)" (ppr ds_expr)
; either_hval <- tryM $ liftIO $
HscMain.hscCompileCoreExpr hsc_env src_span ds_expr
; case either_hval of {
Left exn -> failWithTc (mk_msg "compile and link" exn) ;
Right hval -> do
{
let expr_span = getLoc expr
; either_tval <- tryAllM $
setSrcSpan expr_span $
do { mb_result <- run_and_convert expr_span (unsafeCoerce# hval)
; case mb_result of
Left err -> failWithTc err
Right result -> do { traceTc "Got HsSyn result:" (ppr result)
; return $! result } }
; case either_tval of
Right v -> return v
Left se -> case fromException se of
Just IOEnvFailure -> failM
_ -> failWithTc (mk_msg "run" se)
}}}
where
mk_msg s exn = vcat [text "Exception when trying to" <+> text s <+> text "compile-time code:",
nest 2 (text (Panic.showException exn)),
if show_code then nest 2 (text "Code:" <+> ppr expr) else empty]
\end{code}
Note [Exceptions in TH]
~~~~~~~~~~~~~~~~~~~~~~~
Supppose we have something like this
$( f 4 )
where
f :: Int -> Q [Dec]
f n | n>3 = fail "Too many declarations"
| otherwise = ...
The 'fail' is a user-generated failure, and should be displayed as a
perfectly ordinary compiler error message, not a panic or anything
like that. Here's how it's processed:
* 'fail' is the monad fail. The monad instance for Q in TH.Syntax
effectively transforms (fail s) to
qReport True s >> fail
where 'qReport' comes from the Quasi class and fail from its monad
superclass.
* The TcM monad is an instance of Quasi (see TcSplice), and it implements
(qReport True s) by using addErr to add an error message to the bag of errors.
The 'fail' in TcM raises an IOEnvFailure exception
* So, when running a splice, we catch all exceptions; then for
- an IOEnvFailure exception, we assume the error is already
in the error-bag (above)
- other errors, we add an error to the bag
and then fail
To call runQ in the Tc monad, we need to make TcM an instance of Quasi:
\begin{code}
instance TH.Quasi (IOEnv (Env TcGblEnv TcLclEnv)) where
qNewName s = do { u <- newUnique
; let i = getKey u
; return (TH.mkNameU s i) }
qReport True msg = addErr (text msg)
qReport False msg = addReport (text msg) empty
qLocation = do { m <- getModule
; l <- getSrcSpanM
; r <- case l of
UnhelpfulSpan _ -> pprPanic "qLocation: Unhelpful location"
(ppr l)
RealSrcSpan s -> return s
; return (TH.Loc { TH.loc_filename = unpackFS (srcSpanFile r)
, TH.loc_module = moduleNameString (moduleName m)
, TH.loc_package = packageIdString (modulePackageId m)
, TH.loc_start = (srcSpanStartLine r, srcSpanStartCol r)
, TH.loc_end = (srcSpanEndLine r, srcSpanEndCol r) }) }
qLookupName = lookupName
qReify = reify
qReifyInstances = reifyInstances
qRecover recover main = do { (msgs, mb_res) <- tryTcErrs main
; case mb_res of
Just val -> do { addMessages msgs
; return val }
Nothing -> recover
}
qRunIO io = liftIO io
qAddDependentFile fp = do
ref <- fmap tcg_dependent_files getGblEnv
dep_files <- readTcRef ref
writeTcRef ref (fp:dep_files)
\end{code}
%************************************************************************
%* *
\subsection{Errors and contexts}
%* *
%************************************************************************
\begin{code}
showSplice :: String -> LHsExpr Name -> SDoc -> TcM ()
showSplice what before after
= do { loc <- getSrcSpanM
; traceSplice (vcat [ppr loc <> colon <+> text "Splicing" <+> text what,
nest 2 (sep [nest 2 (ppr before),
text "======>",
nest 2 after])]) }
illegalBracket :: SDoc
illegalBracket = ptext (sLit "Template Haskell brackets cannot be nested (without intervening splices)")
#endif /* GHCI */
\end{code}
%************************************************************************
%* *
Instance Testing
%* *
%************************************************************************
\begin{code}
reifyInstances :: TH.Name -> [TH.Type] -> TcM [TH.Dec]
reifyInstances th_nm th_tys
= addErrCtxt (ptext (sLit "In reifyInstances")
<+> ppr_th th_nm <+> sep (map ppr_th th_tys)) $
do { thing <- getThing th_nm
; case thing of
AGlobal (ATyCon tc)
| Just cls <- tyConClass_maybe tc
-> do { tys <- tc_types (classTyCon cls) th_tys
; inst_envs <- tcGetInstEnvs
; let (matches, unifies, _) = lookupInstEnv inst_envs cls tys
; mapM reifyClassInstance (map fst matches ++ unifies) }
| otherwise
-> do { tys <- tc_types tc th_tys
; inst_envs <- tcGetFamInstEnvs
; let matches = lookupFamInstEnv inst_envs tc tys
; mapM (reifyFamilyInstance . fst) matches }
_ -> bale_out (ppr_th th_nm <+> ptext (sLit "is not a class or type constructor"))
}
where
doc = ClassInstanceCtx
bale_out msg = failWithTc msg
tc_types :: TyCon -> [TH.Type] -> TcM [Type]
tc_types tc th_tys
= do { let tc_arity = tyConArity tc
; when (length th_tys /= tc_arity)
(bale_out (ptext (sLit "Wrong number of types (expected")
<+> int tc_arity <> rparen))
; loc <- getSrcSpanM
; rdr_tys <- mapM (cvt loc) th_tys
; rn_tys <- rnLHsTypes doc rdr_tys
; (tys, _res_k) <- kcApps tc (tyConKind tc) rn_tys
; mapM dsHsType tys }
cvt :: SrcSpan -> TH.Type -> TcM (LHsType RdrName)
cvt loc th_ty = case convertToHsType loc th_ty of
Left msg -> failWithTc msg
Right ty -> return ty
\end{code}
%************************************************************************
%* *
Reification
%* *
%************************************************************************
\begin{code}
lookupName :: Bool
-> String -> TcM (Maybe TH.Name)
lookupName is_type_name s
= do { lcl_env <- getLocalRdrEnv
; case lookupLocalRdrEnv lcl_env rdr_name of
Just n -> return (Just (reifyName n))
Nothing -> do { mb_nm <- lookupGlobalOccRn_maybe rdr_name
; return (fmap reifyName mb_nm) } }
where
th_name = TH.mkName s
occ_fs :: FastString
occ_fs = mkFastString (TH.nameBase th_name)
occ :: OccName
occ | is_type_name
= if isLexCon occ_fs then mkTcOccFS occ_fs
else mkTyVarOccFS occ_fs
| otherwise
= if isLexCon occ_fs then mkDataOccFS occ_fs
else mkVarOccFS occ_fs
rdr_name = case TH.nameModule th_name of
Nothing -> mkRdrUnqual occ
Just mod -> mkRdrQual (mkModuleName mod) occ
getThing :: TH.Name -> TcM TcTyThing
getThing th_name
= do { name <- lookupThName th_name
; traceIf (text "reify" <+> text (show th_name) <+> brackets (ppr_ns th_name) <+> ppr name)
; tcLookupTh name }
where
ppr_ns (TH.Name _ (TH.NameG TH.DataName _pkg _mod)) = text "data"
ppr_ns (TH.Name _ (TH.NameG TH.TcClsName _pkg _mod)) = text "tc"
ppr_ns (TH.Name _ (TH.NameG TH.VarName _pkg _mod)) = text "var"
ppr_ns _ = panic "reify/ppr_ns"
reify :: TH.Name -> TcM TH.Info
reify th_name
= do { thing <- getThing th_name
; reifyThing thing }
lookupThName :: TH.Name -> TcM Name
lookupThName th_name = do
mb_name <- lookupThName_maybe th_name
case mb_name of
Nothing -> failWithTc (notInScope th_name)
Just name -> return name
lookupThName_maybe th_name
= do { names <- mapMaybeM lookup (thRdrNameGuesses th_name)
; return (listToMaybe names) }
where
lookup rdr_name
= do {
; rdr_env <- getLocalRdrEnv
; case lookupLocalRdrEnv rdr_env rdr_name of
Just name -> return (Just name)
Nothing -> lookupGlobalOccRn_maybe rdr_name }
tcLookupTh :: Name -> TcM TcTyThing
tcLookupTh name
= do { (gbl_env, lcl_env) <- getEnvs
; case lookupNameEnv (tcl_env lcl_env) name of {
Just thing -> return thing;
Nothing -> do
{ if nameIsLocalOrFrom (tcg_mod gbl_env) name
then
case lookupNameEnv (tcg_type_env gbl_env) name of
Just thing -> return (AGlobal thing)
Nothing -> failWithTc (notInEnv name)
else do
{ (eps,hpt) <- getEpsAndHpt
; dflags <- getDOpts
; case lookupType dflags hpt (eps_PTE eps) name of
Just thing -> return (AGlobal thing)
Nothing -> do { thing <- tcImportDecl name
; return (AGlobal thing) }
}}}}
notInScope :: TH.Name -> SDoc
notInScope th_name = quotes (text (TH.pprint th_name)) <+>
ptext (sLit "is not in scope at a reify")
notInEnv :: Name -> SDoc
notInEnv name = quotes (ppr name) <+>
ptext (sLit "is not in the type environment at a reify")
reifyThing :: TcTyThing -> TcM TH.Info
reifyThing (AGlobal (AnId id))
= do { ty <- reifyType (idType id)
; fix <- reifyFixity (idName id)
; let v = reifyName id
; case idDetails id of
ClassOpId cls -> return (TH.ClassOpI v ty (reifyName cls) fix)
_ -> return (TH.VarI v ty Nothing fix)
}
reifyThing (AGlobal (ATyCon tc)) = reifyTyCon tc
reifyThing (AGlobal (ACoAxiom ax)) = reifyAxiom ax
reifyThing (AGlobal (ADataCon dc))
= do { let name = dataConName dc
; ty <- reifyType (idType (dataConWrapId dc))
; fix <- reifyFixity name
; return (TH.DataConI (reifyName name) ty
(reifyName (dataConOrigTyCon dc)) fix)
}
reifyThing (ATcId {tct_id = id})
= do { ty1 <- zonkTcType (idType id)
; ty2 <- reifyType ty1
; fix <- reifyFixity (idName id)
; return (TH.VarI (reifyName id) ty2 Nothing fix) }
reifyThing (ATyVar tv ty)
= do { ty1 <- zonkTcType ty
; ty2 <- reifyType ty1
; return (TH.TyVarI (reifyName tv) ty2) }
reifyThing (AThing {}) = panic "reifyThing AThing"
reifyThing ANothing = panic "reifyThing ANothing"
reifyAxiom :: CoAxiom -> TcM TH.Info
reifyAxiom ax@(CoAxiom { co_ax_lhs = lhs, co_ax_rhs = rhs })
| Just (tc, args) <- tcSplitTyConApp_maybe lhs
= do { args' <- mapM reifyType args
; rhs' <- reifyType rhs
; return (TH.TyConI (TH.TySynInstD (reifyName tc) args' rhs') )}
| otherwise
= failWith (ptext (sLit "Can't reify the axiom") <+> ppr ax
<+> dcolon <+> pprEqPred (Pair lhs rhs))
reifyTyCon :: TyCon -> TcM TH.Info
reifyTyCon tc
| Just cls <- tyConClass_maybe tc
= reifyClass cls
| isFunTyCon tc
= return (TH.PrimTyConI (reifyName tc) 2 False)
| isPrimTyCon tc
= return (TH.PrimTyConI (reifyName tc) (tyConArity tc) (isUnLiftedTyCon tc))
| isFamilyTyCon tc
= do { let flavour = reifyFamFlavour tc
tvs = tyConTyVars tc
kind = tyConKind tc
; kind' <- if isLiftedTypeKind kind then return Nothing
else fmap Just (reifyKind kind)
; fam_envs <- tcGetFamInstEnvs
; instances <- mapM reifyFamilyInstance (familyInstances fam_envs tc)
; tvs' <- reifyTyVars tvs
; return (TH.FamilyI
(TH.FamilyD flavour (reifyName tc) tvs' kind')
instances) }
| isSynTyCon tc
= do { let (tvs, rhs) = synTyConDefn tc
; rhs' <- reifyType rhs
; tvs' <- reifyTyVars tvs
; return (TH.TyConI
(TH.TySynD (reifyName tc) tvs' rhs'))
}
| otherwise
= do { cxt <- reifyCxt (tyConStupidTheta tc)
; let tvs = tyConTyVars tc
; cons <- mapM (reifyDataCon (mkTyVarTys tvs)) (tyConDataCons tc)
; r_tvs <- reifyTyVars tvs
; let name = reifyName tc
deriv = []
decl | isNewTyCon tc = TH.NewtypeD cxt name r_tvs (head cons) deriv
| otherwise = TH.DataD cxt name r_tvs cons deriv
; return (TH.TyConI decl) }
reifyDataCon :: [Type] -> DataCon -> TcM TH.Con
reifyDataCon tys dc
= do { let (tvs, theta, arg_tys, _) = dataConSig dc
subst = mkTopTvSubst (tvs `zip` tys)
(subst', ex_tvs') = mapAccumL substTyVarBndr subst (dropList tys tvs)
theta' = substTheta subst' theta
arg_tys' = substTys subst' arg_tys
stricts = map reifyStrict (dataConStrictMarks dc)
fields = dataConFieldLabels dc
name = reifyName dc
; r_arg_tys <- reifyTypes arg_tys'
; let main_con | not (null fields)
= TH.RecC name (zip3 (map reifyName fields) stricts r_arg_tys)
| dataConIsInfix dc
= ASSERT( length arg_tys == 2 )
TH.InfixC (s1,r_a1) name (s2,r_a2)
| otherwise
= TH.NormalC name (stricts `zip` r_arg_tys)
[r_a1, r_a2] = r_arg_tys
[s1, s2] = stricts
; ASSERT( length arg_tys == length stricts )
if null ex_tvs' && null theta then
return main_con
else do
{ cxt <- reifyCxt theta'
; ex_tvs'' <- reifyTyVars ex_tvs'
; return (TH.ForallC ex_tvs'' cxt main_con) } }
reifyClass :: Class -> TcM TH.Info
reifyClass cls
= do { cxt <- reifyCxt theta
; inst_envs <- tcGetInstEnvs
; insts <- mapM reifyClassInstance (InstEnv.classInstances inst_envs cls)
; ops <- mapM reify_op op_stuff
; tvs' <- reifyTyVars tvs
; let dec = TH.ClassD cxt (reifyName cls) tvs' fds' ops
; return (TH.ClassI dec insts ) }
where
(tvs, fds, theta, _, _, op_stuff) = classExtraBigSig cls
fds' = map reifyFunDep fds
reify_op (op, _) = do { ty <- reifyType (idType op)
; return (TH.SigD (reifyName op) ty) }
reifyClassInstance :: Instance -> TcM TH.Dec
reifyClassInstance i
= do { cxt <- reifyCxt theta
; thtypes <- reifyTypes types
; let head_ty = foldl TH.AppT (TH.ConT (reifyName cls)) thtypes
; return $ (TH.InstanceD cxt head_ty []) }
where
(_tvs, theta, cls, types) = instanceHead i
reifyFamilyInstance :: FamInst -> TcM TH.Dec
reifyFamilyInstance fi
| isSynTyCon rep_tc
= do { th_tys <- reifyTypes (fi_tys fi)
; rhs_ty <- reifyType (synTyConType rep_tc)
; return (TH.TySynInstD fam th_tys rhs_ty) }
| otherwise
= do { let tvs = tyConTyVars rep_tc
fam = reifyName (fi_fam fi)
; cons <- mapM (reifyDataCon (mkTyVarTys tvs)) (tyConDataCons rep_tc)
; th_tys <- reifyTypes (fi_tys fi)
; return (if isNewTyCon rep_tc
then TH.NewtypeInstD [] fam th_tys (head cons) []
else TH.DataInstD [] fam th_tys cons []) }
where
rep_tc = fi_tycon fi
fam = reifyName (fi_fam fi)
reifyType :: TypeRep.Type -> TcM TH.Type
reifyType ty@(ForAllTy _ _) = reify_for_all ty
reifyType (TyVarTy tv) = return (TH.VarT (reifyName tv))
reifyType (TyConApp tc tys) = reify_tc_app tc tys
reifyType (AppTy t1 t2) = do { [r1,r2] <- reifyTypes [t1,t2] ; return (r1 `TH.AppT` r2) }
reifyType ty@(FunTy t1 t2)
| isPredTy t1 = reify_for_all ty
| otherwise = do { [r1,r2] <- reifyTypes [t1,t2] ; return (TH.ArrowT `TH.AppT` r1 `TH.AppT` r2) }
reify_for_all :: TypeRep.Type -> TcM TH.Type
reify_for_all ty
= do { cxt' <- reifyCxt cxt;
; tau' <- reifyType tau
; tvs' <- reifyTyVars tvs
; return (TH.ForallT tvs' cxt' tau') }
where
(tvs, cxt, tau) = tcSplitSigmaTy ty
reifyTypes :: [Type] -> TcM [TH.Type]
reifyTypes = mapM reifyType
reifyKind :: Kind -> TcM TH.Kind
reifyKind ki
= do { let (kis, ki') = splitKindFunTys ki
; ki'_rep <- reifyNonArrowKind ki'
; kis_rep <- mapM reifyKind kis
; return (foldr TH.ArrowK ki'_rep kis_rep) }
where
reifyNonArrowKind k | isLiftedTypeKind k = return TH.StarK
| otherwise = noTH (sLit "this kind") (ppr k)
reifyCxt :: [PredType] -> TcM [TH.Pred]
reifyCxt = mapM reifyPred
reifyFunDep :: ([TyVar], [TyVar]) -> TH.FunDep
reifyFunDep (xs, ys) = TH.FunDep (map reifyName xs) (map reifyName ys)
reifyFamFlavour :: TyCon -> TH.FamFlavour
reifyFamFlavour tc | isSynFamilyTyCon tc = TH.TypeFam
| isFamilyTyCon tc = TH.DataFam
| otherwise
= panic "TcSplice.reifyFamFlavour: not a type family"
reifyTyVars :: [TyVar] -> TcM [TH.TyVarBndr]
reifyTyVars = mapM reifyTyVar
where
reifyTyVar tv | isLiftedTypeKind kind = return (TH.PlainTV name)
| otherwise = do kind' <- reifyKind kind
return (TH.KindedTV name kind')
where
kind = tyVarKind tv
name = reifyName tv
reify_tc_app :: TyCon -> [TypeRep.Type] -> TcM TH.Type
reify_tc_app tc tys
= do { tys' <- reifyTypes tys
; return (foldl TH.AppT r_tc tys') }
where
r_tc | isTupleTyCon tc = TH.TupleT (tyConArity tc)
| tc `hasKey` listTyConKey = TH.ListT
| otherwise = TH.ConT (reifyName tc)
reifyPred :: TypeRep.PredType -> TcM TH.Pred
reifyPred ty = case classifyPredType ty of
ClassPred cls tys -> do { tys' <- reifyTypes tys
; return $ TH.ClassP (reifyName cls) tys' }
IPPred _ _ -> noTH (sLit "implicit parameters") (ppr ty)
EqPred ty1 ty2 -> do { ty1' <- reifyType ty1
; ty2' <- reifyType ty2
; return $ TH.EqualP ty1' ty2'
}
TuplePred _ -> noTH (sLit "tuple predicates") (ppr ty)
IrredPred _ -> noTH (sLit "irreducible predicates") (ppr ty)
reifyName :: NamedThing n => n -> TH.Name
reifyName thing
| isExternalName name = mk_varg pkg_str mod_str occ_str
| otherwise = TH.mkNameU occ_str (getKey (getUnique name))
where
name = getName thing
mod = ASSERT( isExternalName name ) nameModule name
pkg_str = packageIdString (modulePackageId mod)
mod_str = moduleNameString (moduleName mod)
occ_str = occNameString occ
occ = nameOccName name
mk_varg | OccName.isDataOcc occ = TH.mkNameG_d
| OccName.isVarOcc occ = TH.mkNameG_v
| OccName.isTcOcc occ = TH.mkNameG_tc
| otherwise = pprPanic "reifyName" (ppr name)
reifyFixity :: Name -> TcM TH.Fixity
reifyFixity name
= do { fix <- lookupFixityRn name
; return (conv_fix fix) }
where
conv_fix (BasicTypes.Fixity i d) = TH.Fixity i (conv_dir d)
conv_dir BasicTypes.InfixR = TH.InfixR
conv_dir BasicTypes.InfixL = TH.InfixL
conv_dir BasicTypes.InfixN = TH.InfixN
reifyStrict :: BasicTypes.HsBang -> TH.Strict
reifyStrict bang | bang == HsUnpack = TH.Unpacked
| isBanged bang = TH.IsStrict
| otherwise = TH.NotStrict
noTH :: LitString -> SDoc -> TcM a
noTH s d = failWithTc (hsep [ptext (sLit "Can't represent") <+> ptext s <+>
ptext (sLit "in Template Haskell:"),
nest 2 d])
ppr_th :: TH.Ppr a => a -> SDoc
ppr_th x = text (TH.pprint x)
\end{code}
Note [Reifying data constructors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Template Haskell syntax is rich enough to express even GADTs,
provided we do so in the equality-predicate form. So a GADT
like
data T a where
MkT1 :: a -> T [a]
MkT2 :: T Int
will appear in TH syntax like this
data T a = forall b. (a ~ [b]) => MkT1 b
| (a ~ Int) => MkT2